I'm not sure why you felt that the SLP was so much softer shooting. After shooting the Versamax, the SLP, and the Benelli with a ComforTech stock; the VersaMax and the Benelli had the least felt recoil (to me).

The Benelli M2 is inertia operated, unlike the other two (and the M4) which are gas operated.

Either of the two guns that you have mentioned would be great....but I will say, the SLP is packaged MUCH better from the factory.